1. Field of the Invention
The present invention relates in general to zinc-bromine battery systems, and, more particularly, to a device and method for the re-acidification of an electrolyte stream in a zinc-bromine flowing electrolyte battery.
2. Background Art
The original concept of utilizing the properties of zinc and bromine in a battery system was patented over 100 years ago in U.S. Pat. No. 312,802. Generally, the battery system has a negative flow loop and a positive flow loop, as well as a separator of some kind in-between. The zinc-bromine electrolyte is circulated through both loops, depositing zinc at the negative electrode, and creating aqueous bromine at the positive electrode, all while creating a voltage difference between the two electrodes. The zinc is collected as a solid, while the aqueous bromine forms a second liquid phase and is separated from the flowing electrolyte.
Utilizing a circulating electrolyte system, Zinc-Bromine batteries have significant advantages, including ease of thermal management and uniformity of reactant due to electrolyte flow, operation of the system at ambient temperature, rapid system charging, complete system discharging, good specific energy of reactants, and a system that is generally constructed from low-cost and readily available materials. The system did not gain immediate commercial acceptance, however, due to the formation of zinc dendrites upon deposition of zinc at the negative electrode, impeding the flow of electrolyte, and due to the solubility of bromine in the zinc-bromine electrolyte, causing a cell short circuit.
In the 1970s, Exxon Corp. and Gould Inc. developed techniques that attempted to inhibit the formation of zinc dendrites upon deposition at the negative electrode. Upon operation, the cell could now be operated for significantly longer periods of time without the previous inhibited flow. The zinc-bromine battery was now a commercially reasonable means of storing and recovering power. However, current operation of zinc-bromine batteries still contain significant problems.
Current operation of a zinc-bromine cell requires specific parameters for continuous operation. Among these requirements is one that the system be operated at or near a pH of two. This requirement exists because at higher pH levels mossy zinc plating develops, as well as bromates within the electrolyte solution. Alternatively, at lower pH values, zinc corrodes at an increasing rate. Although the system reactions do not themselves affect pH, overcharging of the cell during cyclical operation may electrolyze water, creating gaseous hydrogen and hydroxide ions in the water, raising the pH.
Therefore, it is an object of this invention to create a device and method for the re-acidification of the zinc-bromine electrolyte stream in a flowing electrolyte system to, in turn, facilitate longer and more efficient continuous operation of the battery.
It is a further object of this invention to create a means for re-acidification utilizing the products of the current battery system so that an ongoing and steady-state system may be developed.
The present invention is directed to a recombinator device for the re-acidification of an electrolyte stream in a flowing electrolyte zinc-bromine battery. The recombinator device comprises a housing operatively associated with a zinc-bromine battery, means for receiving hydrogen and bromine from the zinc-bromine battery, means for reacting the hydrogen and bromine together so as to form hydrobromic acid, and means for distributing the hydrobromic acid into an electrolyte stream or electrolyte reservoir of the zinc-bromine battery for re-acidification of same.
In a preferred embodiment of the invention, the hydrogen and the bromine receiving means comprises an inlet stream coupling operatively attached to the zinc-bromone battery. In such a preferred embodiment, the hydrobromic distribution means comprises an outlet stream coupling operatively attached to at least one of an electrolyte stream or electrolyte reservoir of the zinc-bromine battery.
In yet another preferred embodiment, the reaction means includes a reaction chamber. In this preferred embodiment, the recombinator device further includes means for facilitating the reaction of hydrogen and bromine within the reaction chamber. Such reaction facilitating means comprises a catalyst which may include a platinized carbon cloth. It is also contemplated that the catalyst include a temperature controller in thermal contact with the housing.
In yet another preferred embodiment, the device includes means for controlling flow of a gas through the housing. In one embodiment, the flow control means comprises positioning of the catalyst in an arrayed spiral configuration within the reaction chamber. The spirals can be separated by spacing means so as to facilitate the flow of a gas therethrough.
In a preferred embodiment of the invention, the flow control means comprises at least a portion of the reaction chamber being constructed from a mesh material.
In another preferred embodiment of the invention, the recombinator device includes means for controlling delivery of bromine into the reaction chamber. In such a preferred embodiment, the delivery control means comprises a capillary operatively associated with the bromine receiving means. Preferably, the capillary is sized to deliver one to two drops of aqueous bromine per minute.
In yet another preferred embodiment, the housing further includes an excess aqueous bromine pool region adjacent the hydrobromic acid distribution means.
The present invention is also directed to a zinc-bromine battery system comprising a zinc-bromine battery having a flowing electrolyte and a recombinator device of the type previously described.
The present invention is further directed to a method for re-acidifying an electrolyte in a flowing electrolyte zinc-bromine battery. The method comprises the steps of: a) introducing an electrolyte stream at least partially comprising aqueous bromine and hydrogen into a reaction chamber; b) reacting the bromine with the hydrogen to create a reaction product, and c) reintegrating the reaction product with at least one of an electrolyte stream or an electrolyte reservoir of the zinc-bromine battery for re-acidification of same.
In a preferred embodiment of the method, the step of introducing further includes the step of controlling the rate of bromine and hydrogen introduced into the reaction chamber. Such a step further includes the step of allowing one to two drops of the hydrogen and bromine electrolyte stream per minute.
In another preferred embodiment, the method further includes the step of regulating the temperature of the housing, and, in turn, the temperature within the reaction chamber. In such an embodiment, the step of regulating the temperature further includes the steps of pre-heating the housing; and maintaining the temperature of the housing. The preferable temperature range is between approximately 100 degrees Celsius and approximately 120 degrees Celsius.
In still another preferred embodiment, the step of reintegrating the reaction product further includes the step of removing the reaction product and excess reactant through an output stream.
In yet another preferred embodiment, the step of reacting the aqueous bromine and hydrogen includes the step of associating same with a catalyst.